A number of methods and apparatus for the control of chromaticity of mixed light emitted from different colour light sources are known in the art. It is also known that the set of single wavelengths or frequencies of the visible or near-visible portions of the electromagnetic spectrum can be expressed as a subset of chromaticity values, known as the spectral locus. Light sources with relatively narrow-band emission spectra such as certain types of light-emitting diodes (LEDs), for example, can be engineered to effectively generate light of a desired chromaticity. Also light from different colour LEDs can be mixed to generate light of a desired chromaticity, provided the desired chromaticity is within the achievable colour gamut. For this purpose different colour LEDs are typically combined with a suitable optical system in the form of a luminaire or fixture. It is known that a suitably designed luminaire that is based on an adequately controlled number of LEDs of different colour, for example, red, green and blue (RGB) LEDs, can generate light of a variety of chromaticities within a gamut defined by the individual chromaticities of the LEDs. It is also known that multi-colour LED based luminaires can also be used to generate white light of variable correlated colour temperature (CCT) as white light is a subset of chromaticities, known as the Planckian locus. The colour rendering index (CRI) of mixed light generated by a multi-colour light source based luminaire can be improved in a number of different ways by adding new light sources with different colours to the luminaire or, within limits, by broadening the spectral bandwidths of one or more of the colour light sources in the luminaire, which, however, may reduce the overall colour gamut of the luminaire. This is specifically relevant for white light sources for which high CRIs are often desirable.
There are a number of systems and methods for the control of multi-colour light sources based luminaires, for example, multi-colour LED based luminaires, known in the art.
For example, International Patent Application Publication No. WO/2007/090283 describes a light source intensity control system and method. The light source comprises one or more first light-emitting elements for generating light having a first wavelength range and one or more second light-emitting elements for generating light having a second wavelength range. The first light-emitting elements and second light-emitting elements are responsive to separate control signals provided thereto. A control system receives a signal representative of the operating temperature from one or more sensing devices and determines first and second control signals based on the desired colour of light and the operating temperature. The light emitted by the first and second light-emitting elements as a result of the received first and second control signals can be blended to substantially obtain the desired colour of light. The desired colour of light generated can thus be substantially independent of junction temperature induced changes in the operating characteristics of the light-emitting elements.
International Patent Application Publication No. WO/2006/105649 describes a white light luminaire with adjustable correlated colour temperature. The luminaire system comprises one or more white light light-emitting elements for generating white light having a particular colour temperature. The system further comprises one or more first colour light-emitting elements and one or more second colour light-emitting elements. The luminaire system mixes the coloured light generated by the first and second colour light-emitting elements with the white light of a particular colour temperature, in order to create white light having a desired correlated colour temperature.
U.S. Pat. No. 7,014,336 describes systems and methods for generating and modulating illumination conditions. The systems and methods for generating and/or modulating illumination conditions can generate high-quality light of a desired and controllable colour, for creating lighting fixtures for producing light in desirable and reproducible colours, and for modifying the colour temperature or colour shade of light within a prespecified range after a lighting fixture is constructed. In one embodiment, LED lighting units capable of generating light of a range of colours are used to provide light or supplement ambient light to afford lighting conditions suitable for a wide range of applications.
United States Patent Application Publication No. 2005/0237733 describes a method and system for controlling lighting to reduce energy consumption of the light sources by changing at least one of the colour rendering index (CRI) and the correlated colour temperature (CCT) while maintaining illumination levels. The method and system sense movement of people in the space relative to light sources that light the space, and automatically and individually adjust plural solid state lighting devices that form each of the respective light sources to a first lighting condition when people are in a first position, wherein the lamps respectively emit light of a first illumination level and a first CRI at a first electrical power level, and to a second lighting condition when people are in a second position, wherein the light sources respectively emit light of the first illumination level and a smaller CRI than the first CRI and at a lower electrical power level than the first electrical power level.
Known methods and apparatus, however, are complex or require a scale-up of the number of components with the number of colours of light sources and therefore can be uneconomical. Therefore, there is a need for a new method and system for controlling multi-colour light sources based luminaires.
This background information is provided to reveal information believed by the applicant to be of possible relevance to the present invention. No admission is necessarily intended, nor should be construed, that any of the preceding information constitutes prior art against the present invention.